Catalyst architecture by control of size, composition, and structure can tune the interaction between metal and support. Support defect sites play a key role in structure manipulation, but often catalytic deactivation is accompanied. Therefore, surface defect control with high durability is essential. Strong metal-support interaction (SMSI) is the one way to tune the surface with durability. The main feature of SMSI is a migration of unstable oxide with substoichiometric surface oxygen concentration to metal nanoparticles, forming thin overlayers. The ideal features of the covering shell are (1) oxide shell needs to be thin and permeable to gaseous species not to suppress the catalytic activity, (2) overlayer should fully encapsulate the metal particles to prevent aggregation, and (3) have high durability in the reaction environment.
Herein, we report a gas-permeable shell formed on Rh nanoparticles with enhanced activity and durability. Fe doping into classic CeO₂(FC) highly facilitated surface oxygen transfer and increased the amount of defect sites, proven with H₂-TPR and Raman spectra. When Rh was deposited on FC and reduced, Rh particles were encapsulated under FC overlayer. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results show that the shell is formed upon reduction and removed upon oxidation reversibly. Cryo-DRIFTS results showed that reactant gases came through the shell and reached the Rh core under the shell. Reverse water-gas shift reaction (RWGS; CO₂ + H₂ → CO + H₂O) occurred on the encapsulated Rh nanoparticles effectively with selective CO formation, unlike bare Rh nanoparticles deposited on ceria produced methane as well. The final structure showed high durability, showing no degradation after 150 hours reaction at high temperature. This investigation proposes that surface defect control of catalyst support is promising strategy for highly durable and gas permeable shell construction.

Table of contents. Scheme of gas permeable Fe-doped CeO<sub>2</sub> shell formed on Rh nanoparticles over Rh nanoparticles.

Table of contents. Scheme of gas permeable Fe-doped CeO₂ shell formed on Rh nanoparticles over Rh nanoparticles.

Gunjoo Kim

Research on surface defect control for metal structure fine-tuning, KAIST

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